Congestive heart failure (CHE) is associated with impaired cardiocyte function. Alterations in the content and isoform distribution of contractile proteins and key proteins involved in calcium handling have been found in CHF. Decreased force development in CHF may result from altered calcium handling, reduced contractile protein function, or from a combination of these factors. The precise relationship between alterations in protein synthesis and impaired cardiocyte function in CHF, however, is still uncertain. The overall goal of the present research proposal is to determine the cellular mechanisms of reduced myocardial function in an experimental animal model of CHF. Our data indicates depressed function at end-stage CHF in both electrically stimulated and in skinned cardiac trabeculae an single skinned cardiocytes. Recent preliminary data, however, indicates that depressed twitch force of contraction precedes depressed myofilament function, suggesting that alterations in calcium handling early in the development of CHF induces depressed cardiac function, while changes in myofilament function are associated with the transition to overt heart failure. In this proposal, therefore, we will specifically test the hypotheses that 1) reduced myocardial force development during the development of CHF is caused by reduced intracellular calcium concentration during systole: Accurate and calibrated intracellular calcium will be measured directly in isolated cardiac trabeculae by fluorescence calcium probe under conditions of strict sarcomere length control using a recently developed technique; 2) The transition to decompensated end-stage CHF is caused by reduced maximum force development, calcium responsiveness, and ATP hydrolysis rate of the contractile apparatus: Force development, calcium responsiveness, and ATP hydrolysis rate will be measured in permeabilized trabeculae as function of free calcium. Laser diffraction techniques will be used to accurately measure and control sarcomere length such that accurate and unambiguous data are obtained. Throughout the development of CHF, calcium handling protein and myofilament protein levels as well as gene expression will be assessed by Western and Northern blot, respectively, to correlate with in-situ functional and hemodynamic data. It is expected that these experiments will provide new and unambiguous data. Accurate knowledge regarding the cellular processes that participate in the development of CHF is critical to the development of innovative treatment strategies aimed to combat this debilitating syndrome.